The development of high energy beams such as the continuous carbon dioxide laser beam has provided a valuable industrial tool with potential in many metal working applications. The ability of this beam to cut, drill and weld a wide variety of materials and metals is well known. However, different applications result in different types of beams being desirable.
For example, certain applications are best carried out with the continuous beam of electromagnetic energy from the laser, while in other applications a pulsed or non-continuous beam is preferred. For example, in gas assisted cutting operations, a continuous beam is generally desirable. However, in certain drilling and welding operations where vaporized metal and other gaseous products of the operation tend to prevent continuous transmission of the beam to the work surface, it is advantageous to perform the work in increments, while alternately removing or blowing away any deleterious gaseous materials which may interfere with the beam. It is the pulsed or non-continuous beam to which the present invention is directed.
It is well known to provide methods of pulsing continuous laser beams, and such methods include the use of rotating mirrors, electromagnetic Q-switching, pump energy modulation and mechanical modulation. Generally, pulse methods involving Q-switching or internal, electrical or electromechanical modifications to the laser or laser supply may compromise the efficiency and power output of the laser in the continuous operating mode, as well as increase the complexity of the circuitry and consequent cost thereof.
Mechanical methods such as slotted rotating disks have been used to physically interrupt a continuous beam from the laser and thereby provide a pulsed beam to a work surface. For example, mechanical beam interruption is shown in British Pat. No. 1,342,436 published Jan. 3, 1974. Since such mechanical elements are exposed to the laser beam, the amount of heat absorbed by the disk for a given power density is a function of the surface reflectivity and cooling. Consequently, such mechanical beam modulators have heretofore been restricted to generally low power lasers. In other words, cooling has been a rather serious problem, and has rendered such mechanical beam modulators unsatisfactory for use with high energy beams.